I applied online. The process took 6 weeks.
HR was incredibly slow. On a good week, you could get an answer once, and on a bad week, you wouldn't get it at all. The technical interview itself was good. The engineers are very qualified, discussed interesting problems, and they were very understanding of people who've never worked with Go. Based on other responses here, I'm still not sure whether they decided to reject me and ghosted, or if they are still considering me.
Past experience, networking in general, etc.
The following metrics were computed from 45 interview experiences for the Monzo Backend Engineer role.
Monzo's interview process for their Backend Engineer roles is very selective, failing most engineers who go through it.
Candidates reported having good feelings for Monzo's Backend Engineer interview process.